docs: define GitHub lifecycle traceability (#34)

[litroc]

Primary issue: #34

Changes

• defines an explicit public-repository allowlist and private-repository fail-closed boundary;
• models immutable identities for repositories, issues/sub-issues, projects, milestones, PRs, reviews, commits, Actions, releases, advisories, artifacts, provenance, tests, and changelogs;
• specifies a bidirectional Goal-to-maintenance lifecycle graph with typed source-backed edges;
• defines issue/project conventions for type, status, labels, milestone, ownership, parent, dependencies, acceptance, and completion evidence;
• establishes deterministic snapshots, lock manifests, caching, pagination, rate-limit handling, retention, and reviewable generation;
• defines least-privilege workflow contexts and clear behavior for stale, missing, malformed, unauthorized, or changing metadata.

Validation

• git diff --check
• npm run lint
• npm run typecheck
• npm run test:content
• npm run build including Pagefind

All checks pass with Node 24.18.0.

Boundaries

• Planning-only; no GitHub permission, workflow, project, or generated index changes.
• Public untrusted workflows may not access, clone, cache, log, or render private repositories.

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[Copilot]

Pull request overview

Adds a new architecture planning document that defines how public GitHub metadata can be used for end-to-end lifecycle traceability (with a fail-closed private-repo boundary), and wires it into the documentation navigation.

Changes:

• Adds an “GitHub integration and lifecycle traceability” architecture document covering allowed sources, immutable identities, lifecycle graph edges, deterministic generation, caching/rate limits, and failure behavior.
• Updates the Architecture sidebar to include the new document.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
sidebars.ts	Adds the new architecture page to the Architecture sidebar navigation.
docs/architecture/github-lifecycle-traceability.md	Introduces the planning record and traceability model for GitHub metadata ingestion and lifecycle linkage.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.